The invention relates to a pin joint for eccentric worm pumps, comprising
an outer joint head including a cavity which is open at least in one axial direction as well as a diametral bore,
an inner joint head disposed in the cavity and likewise including a diametral bore,
a pin extending through both diametral bores, and
pin retaining means to lock the pin at the outer joint head.
Eccentric worm pumps are used frequently in the foodstuff industry because of their characteristic protective conveyance. Conventional eccentric worm pumps, however, have the disadvantage of not leading themselves to cleaning as easily as centrifugal or rotary piston pumps because of their more complicated internal structure. This applies particularly in case of cleaning according to the so-called CIP process (cleaning in place) which must be effected at short intervals for hygienic reasons. With this process a cleansing agent is flushed at high flow rate through the pumps and conduits connected to them, without dismantling them. Areas particularly difficult to clean are those of seals between structural members which are interconnected so as to be disasembled and/or movable with respect to each other in operation. For this reason the joints which usually are provided at both ends of a coupling rod between the drive shaft and the rotor of an eccentric worm pump mainly are designed as open pin joints without any sealing if the pumps are destined for the foodstuff industry.
For instance, DE-A No. 1 528 935 discloses an eccentric worm pump with which two pin joints of the type described initially are arranged at one end each of a tie rod between the drive shaft and the rotor. In each of these joints the pin is formed with a thread at either end, receiving a nut in threaded engagement. The provisions for the design of machinery used in the foodstuff industry, such as the "3A Standard" which is applicable in the U.S.A., do not allow the utilization of threads in the conveying medium. Exceptions exist only for threads having certain rather big radii of curvature which cannot be observed in the case of a joint pin.
Likewise known are pin joints for eccentric worm pumps, for example from DE-B No. 1 278 842, with which the pin is retained by a sleeve which is slid on the outer joint head. The sleeve abuts by its one end on a shoulder of the outer joint head, while its other end is locked against axial displacement by a resiliently caught retaining ring (Seeger circlip). With this design, narrow gaps between the joint head, the sleeve, and the retaining ring are unavoidable so that the design as such is not suitable for cleaning according to the CIP process. The pin joints each are enclosed by a protective sleeve to prevent the material being conveyed from entering into the pin joints. These protective sleeves are made of elastic material and are tightly fixed at the coupling rod between the drive shaft and the rotor, on the one hand, and at the drive shaft or rotor, respectively, on the other hand. Even if they should remain tight, these fixing arrangements present areas which are difficult to clean and exclude cleaning by the CIP process. Therefore, the protective sleeve must be removed and cleaned separately from the associated pin joint if the cleaning is to be at least halfway through. This is an extremely time consuming procedure.
It is, therefore, an object of the invention to design a pin joint of the type specified initially such that it can be cleaned thoroughly in little time and is well suited above all for cleaning according to the CIP process.
This object is met, in accordance with the invention, in that
the pin has two ends projecting radially out of the outer joint head and each formed with a notch transversely of the longitudinal direction of the pin, and
the pin retaining means comprises a helical spring supported at its one end in the two notches formed in the pin and at its other end on a shoulder which is not displaceable in axial direction with respect to the outer joint head.
The two notches formed in the pin may be radiussed such that they can be cleaned easily. Likewise easy to be cleaned is the helical spring, especially by flushing with a cleansing liquid, because of the typical spacing between the individual windings of such a spring. Furthermore, it is easy to disassemble the pin joint, if need be, by pressing the the helical spring away from the joint pin and then pulling out the pin.
In the case of the eccentric worm pump according to DE-A No. 1 528 835 mentioned above, a sliding ring seal is arranged around the drive shaft, it has one portion fixed to the housing and a cup-shaped seal portion which rotates together with the drive shaft thereof. A helical spring is clamped between the latter portion and a shoulder remote from the pin and formed in the outer joint head to press the cup-shaped seal portion against the seal portion which is fixed to the housing. The helical compression spring does not contribute to retain the joint pin.
In accordance with a further development of the invention, by contrast, the shoulder supporting the helical spring which rests on the pin at its other end, is formed at a sliding ring seal which effects sealing between the outer joint head and a housing member.